1. Field of the Invention
The present invention relates to a process for producing a split type mechanical part such as a connecting rod, a cap for the connecting rod, and a split sliding or plain bearing for use, for example, in an internal combustion engine, a piston-type compressor, a piston pump and the like.
2. Description of the Prior Art
In general, a connecting rod has a shape such that a smaller end 6 including a piston pin hole 3 is connected with a larger end 7 including a hole in which a crank-pin of a crankshaft is fitted, as shown in FIG. 1. The larger end 7 is in a half-split state in which it is divided at a mating face (division end face) 5 for easy assembling, and the connecting rod includes a main body section 1 and a cap section 2. The main body section 1 and the cap section 2 are integrally fixed to each other by a bolt passed through a bolt bore which is not shown.
When the main body section 1 and the cap section 2 of the connecting rod are produced, the main body section 1 and the cap section 2 are formed into an integral configuration by casting, forging or the like, and subjected to a cutting and a following processing such as scraping and shaving, or both of the members are separately fabricated by casting or forging and subjected to a scraping and shaving processing or the like.
When the connecting rod is produced in a powder metallurgical process, the main body section and the cap section are compacted and sintered into an integral configuration, and if necessary, the resulting material is subjected to a forging to provide a high density, and then divided into the main body section and the cap section. The following four methods are examples of such dividing methods: 1) a method in which division aiding holes are previously provided in an intended breaking area, and the product is broken at the intended breaking area, as described in Japanese Utility Model Publication No. 47453/82 and Japanese Patent Publication No. 26087/90; 2) a method in which a cutout groove is provided in each of opposite end faces of the intended breaking area, the remaining wall portion is broken, and the resulting members are then cut, as described in Japanese Patent Publication No. 44890/83; 3) a method in which portions having different hardnesses are previously provided in an intended breaking area by a carburizing hardening, and the product is broken at the intended breaking area, thereby providing irregularities on the broken face; and 4) a method in which a groove is previously provided in a molded product at a place to serve as an intended breaking area, and an oxide film is formed in the groove by sintering and forging, and then the product is broken.
In the case of a method of adjusting the degree of true circularness, the size and the shape of a blank such as a cast product, a forged product, a sintered product and the like formed into an integral or divided configuration by cutting or scraping and shaving processing, a high-level processing technique is required and in addition, the number of processing steps is large, and therefore, there is a room for improvement for a reduction in cost.
As compared with a classical producing process including such scraping and shaping, the above-described conventional breaking/dividing method is advantageous in respect of cost, because it includes no step of scraping and shaving the divided end faces. In addition, such method has an advantage that the broken faces can be used directly as mating faces, and irregularities to be meshed with each other are produced on the mating faces and hence, the main body section and the cap section can be positioned.
However, such conventional method has problems that a considerably large breaking load is required for the division, that there is a limit for selection of the material, because a deformation is liable to be produced in the case of a material having a high ductility as in an aluminum alloy, that the product may be broken at a location other than the intended breaking/dividing area, and that there is a room for improvement in the work of positioning during assembling.